a) Field of the Invention
The present invention relates to a gas dynamic pressure bearing apparatus which is structured such that a shaft member and a bearing member are rotatably supported with respect to each other due to gas dynamic pressure action at the space therebetween.
b) Description of the Related Art
Conventionally, there are various applications of dynamic pressure bearing apparatus using a dynamic pressure of fluid in various rotation apparatus. Gas dynamic pressure bearings comprise a gas dynamic pressure bearing portion in the space between a shaft member and a bearing member wherein a dynamic pressure generating groove acts on a gas, such as air, introduced in the gas dynamic pressure bearing portion for pressurizing to generate dynamic pressure such that the shaft member and the bearing member are rotatably supported with respect to each other. Types of gas dynamic pressure bearing apparatus include one in which a gas flows from one end to the other inside a radial gas dynamic pressure bearing portion and one in which a gas flows towards both ends from the center of the radial dynamic pressure bearing portion.
In such a gas dynamic pressure bearing apparatus, it has been conventionally suggested that dust, which enters the apparatus, is captured by a filter as a dust collecting means at a gas suction hole such that burn-out of the gas dynamic pressure bearing portion due to the dust can be prevented; such structures are described in Tokkai H 1-288611, Tokkai H2-11918 and Tokkai H2-113113.
However, the above described conventional apparatus cannot be immediately applied to a rotation apparatus, which requires a highly clean environment, such as a hard disc driving motor. For example, with a hard disc driving motor, since regeneration errors and head crashing can be caused by dust adhering to a surface of a hard disc, the entire device is stored in a drive space which is maintained with a highly clean environment.
Nonetheless, in the above described gas dynamic pressure bearing apparatus, the gas dynamic pressure bearing portion stops in the contacting position right after rotation starts or when the rotation is suspended; consequently, dust due to contacting friction is sucked into the drive space from the gas dynamic pressure bearing portion. As a result, the sucked dust may contaminate the hard disc.
In addition, since the head contacts the hard disc surface right after rotation starts, friction electrifies the hard disc. On the other hand, during stable rotation, the rotating portion of the gas dynamic pressure bearing apparatus, including the hard disc is in the non-contacting position; therefore, the hard disc cannot be grounded. As a result, the electrification loads on the hard disc cannot be removed by grounding such that the head may be damaged.